What is central dogma? From DNA to Protein All proteins consist of polypeptide chains A linear sequence of amino acids Each chain corresponds to the nucleotide base sequence of a gene

What is the first step? 1. Transcription: Enzymes uses base sequence of a gene as template to make strand of RNA Two DNA strands unwind in a specific region RNA polymerase assembles strand of RNA Covalently bonds RNA nucleotides (adenine, guanine, cytosine, uracil) according to nucleotide sequence of exposed gene

What is the second step? 2. Translation Information in the RNA strand is decoded (translated) into a sequence of amino acids

Prokaryotes and eukaryotes In prokaryotic cells (no nucleus) Transcription and translation occur in cytoplasm In eukaryotic cells Genes are transcribed in the nucleus Resulting mRNA is translated in the cytoplasm

Three types of RNA Messenger RNA (mRNA) Carries protein-building codes from DNA to ribosomes Ribosomal RNA (rRNA) Forms ribosomes (where polypeptide chains are assembled) Transfer RNA (tRNA) Delivers amino acids to ribosomes

RNA and DNA compared DNA exists as double-stranded molecules hereditary information double helix contains deoxoyribose sugar RNA Disposable copies of hereditary information and some are catalytic exists as a single stand. contains ribose instead of deoxyribose contains uracil in place of thymine

RNA Modification: Alternative Splicing Before mRNA leaves the nucleus: Introns are removed Some exons are removed along with introns; remaining exons are spliced together in different combinations Poly-A tail is added to 3’ end of new mRNA

What is the genetic code? Messenger RNA (mRNA) carries DNA’s protein-building information to ribosomes for translation mRNA’s genetic message is written in codons Sets of three nucleotides along mRNA strand

Codons Codons specify different amino acids A few codon signals stop translation Sixty-four codons constitute a highly conserved genetic code